Sense amplifiers are employed in a variety of applications to monitor, for example, data signals and provide output signals based on the data signals. In a typical latch-based sense amplifier design for a memory, the sense amplifier enable signal is asserted (i.e., fired) when the bitlines (true and complement) have developed sufficient separation. For example, sufficient separation may be between ten and fifteen percent of the supply voltage (Vcc), but this range may vary depending on various factors (e.g., noise or the technology implemented, such as for the bitcell or sense amplifier).
If the sense amplifier enable signal fires before sufficient separation has developed between the bitlines, erroneous data may be latched in the sense amplifier. Therefore, timing of the sense amplifier enable signal is critical. The enable signal is typically generated using delay chains, with simulations performed across process, temperature, and voltage corners to ensure accurate timing. Despite this, trimming of the sense amplifier delay chain via metal options or laser fuses is often required due to the mismatch between the simulation models and actual silicon implementation.
Various techniques are employed for providing reliable sense amplifier operation in memories, which may include differential amplifiers or conservative latch-based sense amplifier designs. Differential amplifiers may be more robust than latch-based sense amplifier designs, but are typically larger, consume more power, and are slower. Latch-based sense amplifier designs may conservatively allow a greater bitline separation (e.g., thirty percent of the supply voltage) to develop before the sense amplifier enable signal fires, but this reduces the access time and maximum frequency parameters of the design.
For high-speed applications, a cross-coupled latch-based sense amplifier may be employed, for example, with trim capability for the sense amplifier enable signal path. Various techniques are employed for trimming or modifying the sense amplifier enable signal timing, which may include trimming delays utilizing metal options or laser fuses. For example, the delay may be adjusted by removing or adding delay elements using metal options, which may add minimally to die area overhead but may require one or more metal mask changes that adds to the die cost. In addition, each die generally cannot be trimmed separately with different delays. For the laser fuses approach, laser fuses are employed to trim delay chains, which allow each die to be trimmed separately to optimize performance parameters for each die. However, laser fuses occupy substantial die area and expensive laser equipment is generally required to blow the fuses. As a result, there is a need for improved sense amplifier techniques.